Cyclic peptides are basis of many biologically active molecules and examples are found in hormones, antibiotics, toxins, alkaloids, etc. They are important as model compounds for the study of protein conformations. Cyclic peptides occur with different ring sizes and also may contain non-protein amino acids like N-methyl and D-amino acids. Many cyclic peptides are ionophores and take part in active transport of ions across membranes. In this project we plan to study the detailed structure and conformation of a few important selected cyclic peptides by X-ray crystallographic method.